X-Video Motion Compensation (XvMC), is an extension of the X video extension (Xv) for the X Window System. The XvMC

API An application programming interface (API) is a connection between computers or between computer programs. It is a type of software interface, offering a service to other pieces of software. A document or standard that describes how to build ...

allows video programs to offload portions of the

video decoding A video decoder is an electronic circuit, often contained within a single integrated circuit chip, that converts base-band analog video signals to digital video. Video decoders commonly allow programmable control over video characteristics such as ...

process to the

GPU A graphics processing unit (GPU) is a specialized electronic circuit designed for digital image processing and to accelerate computer graphics, being present either as a discrete video card or embedded on motherboards, mobile phones, personal ...

video-hardware. In theory this process should also reduce bus bandwidth requirements. Currently, the supported portions to be offloaded by XvMC onto the GPU are motion compensation (mo comp) and inverse discrete cosine transform (iDCT) for

MPEG-2 MPEG-2 (a.k.a. H.222/H.262 as was defined by the ITU) is a standard for "the generic coding of moving pictures and associated audio information". It describes a combination of lossy video compression and lossy audio data compression methods ...

video. XvMC also supports offloading decoding of mo comp,

iDCT A discrete cosine transform (DCT) expresses a finite sequence of data points in terms of a sum of cosine functions oscillating at different frequencies. The DCT, first proposed by Nasir Ahmed in 1972, is a widely used transformation technique in ...

, and VLD ("Variable-Length Decoding", more commonly known as "slice level acceleration") for not only

but also MPEG-4 ASP video on VIA Unichrome (S3 Graphics Chrome Series) hardware. XvMC was the first UNIX equivalent of the Microsoft Windows DirectX Video Acceleration (DxVA) API. Popular software applications known to take advantage of XvMC include

MPlayer MPlayer is a free and open-source media player software application. It is available for Linux, OS X and Microsoft Windows. Versions for OS/2, Syllable Desktop, Syllable, AmigaOS, MorphOS and AROS Research Operating System are also available. A ...

MythTV MythTV is a free and open-source home entertainment application with a simplified "10-foot user interface" design for the living room TV. It turns a computer with the necessary hardware into a network streaming digital video recorder, a digital ...

, and

xine xine is a multimedia playback engine for Unix-like operating systems released under the GNU General Public License. xine is built around a shared library (xine-lib) that supports different frontend player applications. xine uses libraries fr ...

Device drivers

Each hardware video

capable of XvMC video acceleration requires a

X11 The X Window System (X11, or simply X) is a windowing system for bitmap displays, common on Unix-like operating systems. X originated as part of Project Athena at Massachusetts Institute of Technology (MIT) in 1984. The X protocol has been at ...

software

device driver In the context of an operating system, a device driver is a computer program that operates or controls a particular type of device that is attached to a computer or automaton. A driver provides a software interface to hardware devices, enabli ...

to enable these features.

Hardware manufacturers

Nvidia

There are currently three X11 Nvidia drivers available: a 2D-only

open source Open source is source code that is made freely available for possible modification and redistribution. Products include permission to use and view the source code, design documents, or content of the product. The open source model is a decentrali ...

but obfuscated driver maintained by Nvidia called nv, a

proprietary {{Short pages monitor